This invention relates generally to safety belts and harnesses and to buckles and like fastening mechanisms therefor. More particularly the invention relates to buckles, specifically slide-unlocking type buckles, of safety belts such as seat belts suitable for use in motor vehicles (automobiles), other land craft, sea craft, and aircraft.
Needless to say, safety-belt buckles of the type referred to above must, in order to be commercially salable, meet certain requirements as specified by the safety standards of the countries in which they are to be sold, such as the EEC Rule 77541 of European countries and the MVSS of the United States. Of these requirements, those concerning the strength and durability of buckles are important. Others specify that safety-belt buckles must positively lock two ends of their belt straps in the fastened state and that, moreover, each buckle must be easily and promptly unlockable by a small manipulative force.
For example, the minimum tensile load which a locked buckle must withstand is an acceleration of 33 G (approximately 2.2 tons) depending on the EEC Rule. One requirement for maximum unlocking force is 6 kg for a buckle under tensile load of 30 Kg.
Heretofore, most of the seat-belt buckles have been of the kind comprising a buckle main mechanism secured to the free end of one belt strap and a tongue secured to the free end of an opposite belt strap and adapted to be inserted into the buckle main mechanism for locking. Almost all of the buckles of this character have been of the push-unlocking type, that is, of the type wherein the buckle is unlocked to release the locked tongue by manually pushing a push button. A buckle of this type has an advantageous feature in that it can be made to have a small overall size and a small thickness dimension.
Recently, however, there has been a diversification in the preferences of consumers, and there is a considerable demand not only for seat-belt buckles of the push-unlocking type but also for buckles of various other types.